This invention pertains generally to optical radars and particularly to optical radars which may be carried by a person and used as a rangefinder.
It is well known in the art that an optical radar may be used as a rangefinder. When, however, it is required that such a radar be compact and simple enough to be housed in a structure resembling ordinary field glasses, many problems are encountered which cannot be solved by conventional techniques. In particular, in the receiver of such a system it is not feasible to use any of the many known types of photosensitive detectors which require cryogenic cooling for satisfactory operation. Such a stricture, in turn, means that, at present, only a photomultiplier, a silicon p-i-n photodiode or a silicon avalanche photodiode (referred to hereinafter simply as an avalanche photodiode) may be used.
While the avalanche photodiode has the advantage of greater sensitivity than either a photomultiplier or a p-i-n photodiode, the characteristics of such a photodiode change radically with any change in ambient temperature or bias voltage. In particular, the amount of internally generated noise (sometimes referred to as "pop" noise) is dependent upon both ambient temperature and bias voltage. As a result, then, satisfactory operation of such a photodiode may not be achieved unless special provisions are taken to compensate for the effects induced by changes in temperature and bias voltage.